Manufacturers and users of curable formulated products such as adhesives, sealants, coatings and molded articles have an ongoing interest in products that cure faster and with less energy input in addition to their interest in simplifying formulating and storage as well as easing handling. Several types of curable systems have been found by applicants to experience advantages when cured by certain types of amino-polyamides. Particular systems where these new curatives have been found to be especially useful include epoxies, polysulfides and cyanoacrylates.
U.S. Pat. No. 5,231,147, issued to applicants on Jul. 27, 1993, discloses a one-component polyurethane adhesive system useful for bonding together products used in the construction of various materials. This patent describes dispersing a polyamide resin into a polyurethane to form a composite, and then activating the composite by heating to form, by curing, an adhesive composition. The polyurethane base and the polyamide curing agent are mixed together and remain stable prior to activation.
Epoxy, polysulfide and cyanoacrylate chemistry is currently utilized in producing numerous types of adhesive, sealant and other products.
I. Epoxy resins are organic materials (including oligomers or polymers) that contain at least two epoxide functional groups. A respresentative epoxy formula follows: ##STR1## R.sub.1 may be any alkyl, aryl or other moiety in various combinations. Epoxies have been cured with liquid amines, liquid amine-functional polyamides or solid or liquid latent curatives, usually of an amine type. In most systems, the liquid amine or polyamide curative is used as a second component from the epoxy base since reaction begins upon mixing. There exists a general inability by most manufacturing companies to formulate single component products with these curatives. In addition, sustained oven post-curing may also be required.
Types of epoxy resins include:
a) Polyglycidyl and poly(.beta.-methylglycidyl) esters which can be obtained by reacting compounds containing two or more carboxyl groups with epichlorohydrin, glycerol dichlorohydrin or .beta.-methylepichlorohydrin in the presence of alkaline substances.
Examples of compounds with at least two carboxyl groups include aliphatic polycarboxylic acids, cycloaliphatic polycarboxylic acids and aromatic polycarboxylic acids. Particular examples of tricarboxylic and higher carboxylic acids are: aromatic tricarboxylic or tetracarboxylic acids, such as trimellitic acid, trimesic acid, pyromellitic acid or benzophenonetetracarboxylic acid, dimerized or trimerized fatty acids, and copolymers of (meth)acrylic acid with copolymerizable vinyl monomers, for example the 1:1 copolymers of methacrylic acid with sytrene or with methyl methacrylate.
b) Polyglycidyl and poly(.beta.-methylglycidyl) ethers which can be obtained by reacting a compound containing two or more alcoholic hydroxyl groups and/or phenolic hydroxyl groups with epichlorohydrin, glycerol dichlorohydrin or .beta.-methylepichlorohydrin under alkaline conditions, or if in the presence of an acid catalyst, the treating of the resultant product with alkali.
Examples of compounds with two or more alcoholic hydroxyl groups and/or phenolic hydroxyl groups are aliphatic or cycloaliphatic alcohols, and alcohols containing aromatic groups, such as N,N-bis(2-hydroxyethyl) aniline or p,p'-bis(2-hydroxyethylamino)diphenylmethane, or mononuclear or polynuclear phenols, such as resorcinol, hydroquinone, bis(4-hydroxyphenyl)methane, 2,2-bis(4-hydroxyphenyl) propane, brominated 2,2-bis(4-hydroxyphenyl)propane, bis(4-hydroxyphenyl)ether, bis(4-hydroxyphenyl)sulfone, 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane or novolacs which can be obtained by condensing aldehydes, such as formaldehyde, acetaldehyde, chloral or furfuraldehyde, with unsubstituted, alkyl-substituted or halogen-substituted phenols.
c) Poly(S-glycidyl) compounds, including di-S-glycidyl derivatives which are derived from dithiols, such as ethane-1,2-dithiol, or from bis(4-mercaptomethylphenyl) ether.
d) Poly(N-glycidyl) compounds which can be prepared by dehydrochlorinating reaction products of epichlorohydrin with amines which contain at least two amino hydrogen atoms.
Examples of amines on which such epoxy resins are based are aliphatic or cycloaliphatic amines, aromatic amines, such as aniline, p-toluidine, bis(4-aminophenyl)methane, bis(4-aminophenyl)sulfone or bis(4-aminophenyl) ether, or araliphatic amines, such as m-xylylenediamine.
The poly(N-glycidyl) compounds also can include triglycidyl isocyanurate, N,N'-diglycidyl derivatives of cycloalkyleneureas such as ethyleneurea or 1,3-propyleneurea, and N,N'-diglycidyl derivatives of hydantoins such as 5,5-dimethylhydantoin.
e) Cycloaliphatic epoxy resins or epoxidation products of dienes or polyenes, such as cycloaliphatic epoxy resins which are prepared in preferred embodiments by epoxidizing ethylenically unsaturated cycloaliphatic compounds. Examples are, 2,3-epoxycyclopentyl glycidyl ether, 1,2-bis(2,3-epoxycylopentoxy)ethane, diglycidyl cyclohexane-1,2-dicarboxylate, 3,4-epoxycyclohexyl glycidyl ether, bis(3,4-epoxycyclopentyl)ether, bis(2,3-epoxycyclopentyl)ether, dicyclopentadiene dioxide and 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate.
It is also possible to cure epoxy resins in which the 1,2-epoxy groups are bonded to different heteroatoms or functional groups; for example, the N,N,O-triglycidyl derivative of 4-aminophenol, the glycidyl ether glycidyl ester of salicylic acid, and 2-glycidyloxy-1,3-bis(5,5-dimethyl-1-glycidylhydantoin-3-yl)propane.
Various prior art epoxy systems have used amine or amine-type curatives. The vast majority of such systems are two-part systems which cure immediately when two different components are mixed. See, for example, U.S. Pat. Nos. 5,001,193, 4,914,164, 4,751,278, 4,484,004, 4,460,790, 4,322,321, 4,277,621 and 4,150,229. Similarly, polysulfide systems using amine and nitrogen curatives are known. See, for example, U.S. Pat. Nos. 4,542,183 and 4,067,842. Cyanoacrylate non-latent systems using amino catalysts or amine materials exist. See U.S. Pat. Nos. 4,702,783 and 3,940,362.
U.S. Pat. No. 4,322,321 describes one or more curing systems for epoxy resins utilizing a polyamide as a curative but the curative reacts readily. U.S. Pat. No. 3,755,261 shows the curing of amine-curable polymers with salts of aromatic diamines. U.S. Pat. No. 4,914,164 discloses processes using polyamidoamines as curatives for epoxy resins involving very long cure times.
It would be highly desirable to develop a epoxy curing system utilizing amino-terminated polyamides which would be stable and latent until the introduction of external activation to initiate cure.
Many known one-component, heat-curable adhesive compositions require sustained heating, and possibly fixturing, to cure. Therefore, heat sensitive substrates generally cannot be used with such heat-curable adhesives.
U.S. Pat. No. 5,073,601 involves the use of a polyamide as a backbone component in a epoxy system requiring long heat time. U.S. Pat. No. 4,506,099 describes specific liquid diamines used as curing agents for epoxy resins.
The need for latent epoxy adhesive curatives involving polyamine or amine-epoxy adducts and a proposed solution is described in an article appearing on pages 17 to 20 of Adhesives Age for June, 1992. Finely-divided, amine-type solid hardeners dispersed in liquid epoxy, likely as solid latent polyamides of a cyclic tetra-amide type, are discussed in an article appearing on pages 186 to 192 of the October, 1985 issue of Modern Paint and Coatings.
Two recent U.S. patents issued to Ciba Geigy Corporation are of particular interest. U.S. Pat. No. 5,138,078 describes a curing agent for a thermosetting coating and casting composition which is selected from the group consisting of dicyandiamide, the carboxylic acid functional thermosetting polyesters, the phenolic terminated polyhydroxyethers, the amines and the anhydrides.
German Patent Application DE 3246267 A1 published on Jun. 30, 1983 discloses latent epoxy curing agents utilizing amino-diamide curing compositions. The patent describes a synthesis process involving purification and/or extraction steps for eliminating highly reactive mono-amides from the curatives disclosed and discloses curing times of at least from ten to sixty minutes at temperatures of 100-150.degree. C.
II. Polysulfides are prepolymers that contain at least two mercaptan functional groups. A representative polysulfide formula follows: EQU HSR.sub.3 SH
R.sub.3 may be any alkyl, aryl or other moiety in various combinations. Polysulfides are generally cured by certain metal peroxides or dichromates. If formulation of single-component systems is desired, less reactive peroxides such as calcium peroxide or zinc peroxide have been selected. These curatives become activated in the presence of relatively alkaline materials such as atmospheric moisture. These single component formulations cure very slowly, and depend on diffusion of the activating material through the curable mass. Such prior art systems generally cure on their outer surfaces initially; then, very gradually, the curing progresses toward the inner regions. Two-component systems have generally been used by manufacturers in actual practice to produce commercial products.
Certain polysulfide compositions can be cured in the presence of moisture. For instance, U.S. Pat. No. 3,659,896 describes an automobile windshield mounting and sealing means that is provided by a preformed, adhesive, curable sealing strip comprising a thiol terminated synthetic polymer, particularly a liquid polysulfide polymer. The polymer cures in the presence of atmospheric moisture under ambient room temperature and weather conditions.
A curable polysulfide base shown in the art can also be a prepolymer having a plurality of mercaptan functionality that can be cured by certain peroxides in the presence of relatively alkaline materials such as atmospheric water. Such prepolymers may be prepared by techniques as described in the Kirk-Othmer Encyclopedia of Chemical Technology, Third Edition, Volume 18, p. 825. The prepolymers have an average molecular weight of from about 300 to about 8,000. Typical polysulfide prepolymers may be obtained from Morton Thiokol, Inc., Chicago, Ill. and are described in their brochure "LP Liquid Polysulfide Polymer". Additional illustrative polysulfide systems are described in U.S. Pat. Nos. 3,659,896 and 3,714,132, the contents of all of this information being incorporated by reference.
While calcium peroxide and zinc peroxide are preferred, additional compounds which can be used are lead peroxide, cadmium peroxide, magnesium peroxide, ammonium dichromate, potassium dichromate, sodium dichromate and others. The amount of peroxide or dichromate included in the composition is from about 2 to about 35 parts by weight, based upon 100 parts by weight of polysulfide prepolymer.
III. A still further type of system curable using the compounds of this invention as described hereafter is the polymerization of alpha-cyanoacrylic acid esters (also known as 2-cyanoacrylic esters) which polymerize in the presence of basic materials such as water. A representative formula for such esters follows: ##STR2## R.sub.4 may be any alkyl, aryl or other moiety in various combinations, particularly an alkyl group containing from 1 to 4 carbon atoms.
Preferred alpha-cyanoacrylic acid ester systems use methyl-2-cyanoacrylate, ethyl-2-cyanoacrylate, propyl-2-cyanoacrylate, isopropyl-2-cyanoacrylate, butyl-2-cyanoacrylate and isobutyl-2-cyanoacrylate. Such esters are commercially available from Eastman Kodak Co., Loctite Corp., Schering Industrial Chemicals, and Henkel Corporation among others. Additional information concerning cyanoacrylic ester polymers may be found in the Kirk-Othmer Encyclopedia of Chemical Technology, Third Edition, Vol. I, p. 408-413, the contents of which are incorporated by reference.